An ink-jet recording method, in which information is recorded onto a recording material (hereafter, occasionally abbreviated as a medium) by controlled ejection of an ink onto the recording material without contact of a recording head with the recording material, exhibits advantages such as low noise, high-speed printing, capability of recording onto plain paper sheets, and the like.
As the ink-jet recording ink which is applied in the ink-jet recording method mentioned above, those which have been known and have been employed are composed of, as main components, various kinds of dyes or pigments, and water or a water-soluble solvent which dissolves or disperses those dyes or pigments, and various kinds of additives, as desired.
Such ink-jet recording inks are required to provide for:
(1) No clogging to be caused in the nozzle of the ink-jet recording head PA0 (2) Appropriate physical properties to be possessed so as to meet ink ejection characteristics (flying stability, frequency response, etc.) PA0 (3) Ink-jet recording ink to be non-corrosive to materials in contact PA0 (4) Stability is secured over long-term storage PA0 (5) Stable re-ejection after long-term suspension of printing is secured PA0 (6) Rapid drying ink PA0 (7) Good printing quality PA0 (8) Good image retention qualities (light fastness, water resistance, etc.)
Furthermore, the following characteristics are required when the ink-jet recording ink is employed for printing onto a recording material:
In order to fully meet the above-mentioned requirements, it is necessary for contradicting characteristics to coexist such as, for example, rapid drying after printing described in (6), while preventing drying of the ink in the nozzle during suspension of printing so as to meet the requirement described in (1).
Drying of ink in the nozzle during suspension of printing may be prevented by addition of a large amount of a water-soluble high-boiling point organic solvent. However, by so doing, the water-soluble high-boiling point organic solvent remains on the medium after printing, and the image is likely to be deteriorated during storage. Furthermore, in order to prevent deposition of dye, it has been proposed to decrease the amount of divalent ions or inorganic ions. However, the effect has been insufficient for the high concentration of the dye. In addition, because ink for continuous use requires electric conductivity of more than a specific value, an inorganic ion is frequently added.
Furthermore, Japanese Patent Publication Open to Public Inspection No. 62-181372 discloses a method in which the ink during suspension of printing is gelled to prevent drying ink. However, ink comprising a gelling agent is not absorbed quickly into a medium and therefore tends to degrade the image quality. Japanese Patent Publication Open to Public Inspection No. 5-148437 discloses a method in which an organic acid salt having an amine derivative and a hydroxyl group is added to an ink. However, when an inorganic salt is added together, no sufficient effect is obtained.
Conventionally, a number of ink-jet recording inks have been proposed. However, none have yet all the requirements mentioned above.